The invention relates generally to radio frequency transceivers and, more particularly, to transceivers having a transmitter and a receiver that share a common antenna.
It is often desirable to have a radio frequency (RF) transmitter and receiver share a common antenna. This practice reduces the overall cost of implementing an RF system by eliminating one antenna. It also ensures that the transmit and receive beams of the system are identical. A number of challenges arise, however, in implementing a shared antenna arrangement. For example, during transmit operations, the relatively high transmit power generated by the transmitter cannot be permitted to overload the front end of the receiver. In addition, during a receive operation, the received signal must be directed from the antenna to the receiver input with little loss in the intervening circuitry. Furthermore, both the transmitter and the receiver must be appropriately matched to the antenna during transmit and receive operations, respectively, to enhance power transfer between these elements. Duplexer structures are normally employed to address these issues.
An ongoing trend in the electronics industry is to integrate entire systems or subsystems onto a single semiconductor chip using, for example, very large scale integration (VLSI) techniques. Because of its characteristic low power consumption, low cost, and high integration density, complementary metal-oxide-semiconductor (CMOS) technology is often used to achieve this integration. The integration of RF transceiver subsystems, however, has thus far presented a major challenge to circuit designers. This is because RF transceivers typically make extensive use of passive components (e.g., inductors and capacitors) which are not easily implemented on a semiconductor chip. Another reason is because RF transceivers are generally required to detect very small signals from an antenna which can be obscured by, for example, digital switching noise when the RF circuitry is implemented on the same chip as digital circuitry performing control and signal processing functions for the transceiver. This is especially true for RF transceiver subsystems that utilize antenna sharing.